Doctor Who season 12 brought back the TARDIS crew in stunning fashion, and the teaser for episode 2 even includes a well-hidden Easter egg referencing a past version of the Master. Returning on New Year's Day 2020, Doctor Who's "Spyfall" brought back Yaz, Ryan and Graham, as well as Jodie Whittaker's Thirteenth Doctor, on a spy-flavored adventure that ended on a game-changing twist. Spies all across Earth are being targeted by mysterious formless aliens that even the Doctor can't identify, and one even nearly breaches the famously impenetrable TARDIS. Recruited by MI6 to rectify the situation, the Doctor finds herself outmatched and overpowered by her new enemy, discovering precious little about their origins or intentions.
Crucially, the Doctor is also outsmarted, but only thanks to the presence of her best Time Lord enemy, the Master. Last seen dying permanently in "The Doctor Falls," Michelle Gomez portrayed the most recent incarnation of the villain, before being offed by her John Simm-shaped predecessor. Nothing has been seen of the Master since, but the character has now returned, played by Sacha Dhawan. Having already infiltrated MI6, the Master became an acquaintance of the Doctor's while hatching a currently-unknown scheme with the aforementioned new alien species. This dastardly plan is now being put into motion, and the Master reveled in witnessing the Doctor's sheer shock as she caught on to the deception.
Next week's episode will pick up directly where "Spyfall" left off, with the Doctor trapped in a strange, unknown location, and her companions crashing to Earth in what's left of the Master's plane. The teaser for episode 2 highlights the Master seemingly arranging for the Doctor's death, a new Victorian-era setting and the return of Lenny Henry's mysterious Daniel Barton. However, the footage is repeatedly punctuated by a hand (likely belonging to Dhawan's Master) hitting a telegraph button in a rhythmic four-beat phrase that will be ominously familiar to Doctor Who fans. This exact drumbeat is a direct reference to the sound of drums storyline introduced during John Simm's time as the Master.
While facing off against David Tennant's Tenth Doctor, the Master claims that he's heard a constant drumming noise in his head ever since childhood, which has slowly driven him insane. As is his nature, the Doctor promises to try and help cure his rival, but eventually discovers that this soul-crushing rhythm was intentionally placed into the Master's mind by the Time Lords as a means of escaping and surviving the Time War. In "The End of Time," both the Doctor and the Master team up to stop this plan from succeeding. In a neat touch, the telegraph hammering in Doctor Who's latest teaser is the exact same rhythm and timing as the old "sound of drums" John Simm's Master so often complained about.
It remains to be seen whether the return of the sound of drums in Doctor Who's latest teaser is merely a fun, fan-pleasing Easter egg to help celebrate the Master's grand comeback or whether there are deeper story implications yet to come. Incarnations of the Master traditionally appear in regeneration order, but Sacha Dhawan's iteration could be an older regeneration that sits perhaps between the Doctor Who movie's Eric Roberts and new-Who's Derek Jacobi. Since the Master was eventually cured of the mental drumming affliction, this might explain why episode 2 of season 12 is still playing the same old beat.
Doctor Who season 12 continues with "Spyfall Part 2" January 5th on BBC and BBC America.